(1) Field of the Invention
The present invention relates to a one-chip semiconductor device such as a one-chip microcomputer incorporating a power-supply-potential detecting circuit for resetting the device when the power supply potential is lower than a predetermined value.
(2) Description of the Prior Art
In a semiconductor device or integrated circuit such as a one-chip microcomputer, if the rated power supply potential is 5 V, the device normally operates at its rated accuracy in the range of .+-.5% to .+-.10% of the rated potential. When the power supply potential deviates from the above-mentioned range, the device may perform a logically erroneous operation and may overrun.
To prevent the device from erroneously operating, a power-supply-potential detecting circuit is provided. When the power supply potential becomes lower than a detection potential of the circuit, the circuit generates a signal for resetting the device.
In a one-chip semiconductor device incorporating such a power-supply-potential detecting circuit, it is naturally checked whether the device operates normally in the predetermined range of the rated power supply potential. In addition, it is necessary to check whether the device operates normally when the power supply potential is between the lower limit of the above-mentioned range and the detection potential, since customers may use the device below the lower limit.
In the above-mentioned one-chip semiconductor device incorporating such a power-supply-potential detecting circuit, however, there is an area between the lower limit of the above-mentioned range and the detection potential of the power-supply-potential detecting circuit which cannot be checked. For example, if the detection potential of the circuit is about 4.0 V, the circuit can check whether the device operates normally only when the power supply potential is higher than, 4.1 V due to the manufacturing fluctuation. That is, the area between 4.0 V to 4.1 V cannot be checked.